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tamaranim1 [39]
3 years ago
5

The door is 3.00 m tall and 1.25 m wide, and it weighs 750 N . You can ignore the friction at the hinges. If Exena applies a for

ce of 220 N at the edge of the door and perpendicular to it, how much time does it take her to close the door?
Physics
1 answer:
Marat540 [252]3 years ago
4 0

Answer:

0.674 s = t

Explanation:

Assuming that the door is completely open, exena need to rotate the door 90°.

Now, using the next equation:

T = I∝

Where T is the torque, I is the moment of inertia and ∝ is the angular aceleration.

Also, the torque could be calculated by:

T = Fd

where F is the force and d is the lever arm.

so:

T = 220N*1.25m

T = 275 N*m

Addittionaly, the moment of inertia of the door is calculated as:

I = \frac{1}{3}Ma^2

where M is the mass of the door and a is the wide.

I  =\frac{1}{3}(750/9.8)(1.25)^2

I = 39.85 kg*m^2

Replacing in the first equation and solving for ∝, we get::

T = I∝

275 = 39.85∝

∝ = 6.9 rad/s

Now, the next equation give as a relation between θ (the angle that exena need to rotate) ∝ (the angular aceleration) and t (the time):

θ = \frac{1}{2}∝t^2

Replacing the values of θ and ∝ and solving for t, we get:

\sqrt{\frac{2(\pi/2)}{6.9 rad/s}} = t

0.674 s = t

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As a pelican flies through the air, it flaps its wings, thereby pushing down on the air below. What is the reaction force?
madam [21]

Answer:

the reaction force in this situation would be B

Explanation:

The action is the wings pushing down whilst the reaction is the air pushing up which allow the bird to fly .

plz mark brainliest to help me lvl up :P

7 0
3 years ago
Read 2 more answers
Please help, I do not understand
Anettt [7]
I think the key here is to be exquisitely careful at all times, and
any time we make any move, keep our units with it.

We're given two angular speeds, and we need to solve for a time.

Outer (slower) planet:
Angular speed =  ω  rad/sec
Time per unit angle =  (1/ω)  sec/rad
Angle per revolution = 2π rad
Time per revolution = (1/ω sec/rad) · (2π rad) = 2π/ω seconds .

Inner (faster) planet:
Angular speed =  2ω  rad/sec
Time per unit angle =  (1/2ω)  sec/rad
Angle per revolution = 2π rad
Time per revolution = (1/2ω sec/rad) · (2π rad) = 2π/2ω sec = π/ω seconds.

So far so good.  We have the outer planet taking 2π/ω seconds for one
complete revolution, and the inner planet doing it in only π/ω seconds ...
half the time for double the angular speed.  Perfect !

At this point, I know what I'm thinking, but it's hard to explain.
I'm pretty sure that the planets are in line on the same side whenever the
total elapsed time is something like a common multiple of their periods.
What I mean is:

They're in line, SOMEwhere on the circles, when

     (a fraction of one orbit) = (the same fraction of the other orbit)    
AND
     the total elapsed time is a common multiple of their periods.

Wait !  Ignore all of that.  I'm doing a good job of confusing myself, and
probably you too.  It may be simpler than that.  (I hope so.)  Throw away
those last few paragraphs.

The planets are in line again as soon as the faster one has 'lapped'
the slower one ... gone around one more time.  
So, however many of the longer period have passed, ONE MORE
of the shorter period have passed.  We're just looking for the Least
Common Multiple of the two periods.

      K (2π/ω seconds)  =  (K+1) (π/ω seconds)

                     2Kπ/ω   =    Kπ/ω + π/ω

Subtract  Kπ/ω :    Kπ/ω = π/ω

Multiply by  ω/π :      K  =  1

(Now I have a feeling that I have just finished re-inventing the wheel.)

And there we have it:

     In the time it takes the slower planet to revolve once,
     the faster planet revolves twice, and catches up with it.
    
     It will be  2π/ω  seconds before the planets line up again.
    
     When they do, they are again in the same position as shown
     in the drawing.

To describe it another way . . . 

     When Kanye has completed its first revolution ...

     Bieber has made it halfway around.

     Bieber is crawling the rest of the way to the starting point while ...

     Kanye is doing another complete revolution.

     Kanye laps Bieber just as they both reach the starting point ...

     Bieber for the first time, Kanye for the second time.


You're welcome.  The generous bounty of 5 points is very gracious,
and is appreciated.  The warm cloudy water and green breadcrust
are also delicious.
5 0
3 years ago
The critical angle between a medium and air is 430. What is the speed of light in that medium?
vagabundo [1.1K]

Answer:

The speed of light is that medium is 281907786.2 m/s.

Explanation:

since the critical angle is Фc = 430, we know that the refractive index is given by:

n = 1/sin(Фc)

  = 1/sin(430)

  = 1.06

then if n is the refractive index of the medium and c is the speed of light, then the speed of light in the medium is given by:

v = c/n

  = (3×10^8)/(1.06)

  = 281907786.2 m/s

Therefore, the speed of light is that medium is 281907786.2 m/s.

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3 years ago
When does a ball that is thrown vertically upwards reach its maximum speed?
ladessa [460]
As soon as you let go of it it is at its max speed because gravity is constantly pulling it down
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A charged balloon will stick to a neutral wall. which process is involved?
Leokris [45]
<span>The charged balloon will stick to a neutral wall because of the Static Electricity:
</span>
 The matter is formed by atoms and these atoms are composed of electrons, protons and neutrons (the electrons have a negative charge, the protons have a positive charge and the neutrons have no charge).

 As the balloon is charged (It gained electrons), and the charge of the same sign repel each other, when it approaches the wall, the electrons of this wall will move away, and the positive charges (protons) will remain in the nearest area to the balloon. As the charges of different signs are attracted, the balloon will be stuck to the wall.
3 0
3 years ago
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